Microporous polyolefin composite film with a thermally stable porous layer at high temperature

Abstract

Provided is a microporous polyolefin composite film with a thermally stable porous layer at high temperature, particularly, to the microporous polyolefin composite film in which the thermally stable porous layer at high temperature, which contains organic or inorganic particles and heat-resistant polymer having aromatic ring in main chain and also having a melting temperature or a glass transition temperature of 170 to 500° C., is formed on one surface or both surfaces of a polyolefin microporous film by a phase separation, wherein the composite film with the porous layer has a permeability of 1.5×10 −5 to 20.0×10 −5 Darcy, a meltdown temperature of 160 to 300° C., a MD/TD shrinkage of 1 to 40% at a temperature of 150° C. for 60 minutes.

The invention claimed is: 
     
       1. A microporous polyolefin composite film in which a thermally stable porous layer, which contains organic or inorganic particles and heat-resistant polymer having aromatic ring in main chain and also having a melting temperature or a glass transition temperature of 170 to 500° C., is formed on one surface or both surfaces of a polyolefin microporous film by a phase separation with a non-solvent, wherein the composite film with the porous layer has a permeability of 1.5×10 −5  to 20.0×10 −5  Darcy, a meltdown temperature of 160 to 300° C., a MD/TD shrinkage of 1 to 40% at a temperature of 150° C. for 60 minutes,
 wherein the heat-resistant polymer is selected from a group consisting of polycarbonate, polyacrylate, and a mixture thereof, 
 the organic or inorganic particles have a size of 0.01 to 2 μm, 
 the organic particles are selected from a group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyurethane, polymethylpentene (PMP), polyethylene terephthalate (PET), polycarbonate (PC), polyester, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polymethylene oxide (PMO), polymethyl methacrylate (PMMA), polyethylene oxide (PEO), cellulose, and a mixture thereof, and the inorganic particles are selected from a group consisting of an oxide, a hydroxide, a sulfide, a nitride, a carbide and a mixture thereof of at least one of metallic or semiconductor elements comprising Si, Al, Ca, Ti, B, Sn, Mg, Li, Co, Ni, Sr, Ce, Zr, Y, Pb, Zn, Ba, and 
 the content of organic or inorganic particles is 2-20 wt % based on the solution coated on the polyolefin microporous film, the content of heat-resistant polymer is 2-20 wt % based on the solution coated on the polyolefin microporous film, and a remainder of the solution being a solvent and the non-solvent. 
 
     
     
       2. The microporous polyolefin composite film according to  claim 1 , wherein the thermally stable porous layer has a thickness which is 0.1 to 1.0 times that of the polyolefin microporous film, and a bonding force between the porous layer and the polyolefin microporous film is 0.1 to 1.0 kgf/cm. 
     
     
       3. The microporous polyolefin composite film according to  claim 1 , wherein the polyolefin microporous film is selected from a group consisting of polyethylene, polypropylene, polybutylene, a copolymer thereof, and a mixture thereof. 
     
     
       4. The microporous polyolefm composite film according to  claim 1 ,
 wherein the surface of the polyolefin microporous film is treated by ionizing radiation or plasma. 
 
     
     
       5. A separator for a lithium secondary battery, comprising the microporous composite film according to  claim 1 . 
     
     
       6. A secondary battery comprising the separator according to  claim 5 .